1. Field of the Inventions
The inventions relate to systems and methods for ablating tissue such as, for example, systems and methods for ablating myocardial tissue for the treatment of cardiac conditions.
2. Description of the Related Art
Physicians make use of catheters and other devices today in medical procedures to gain access into interior regions of the body to ablate targeted tissue areas. It is important for the physician to be able to precisely locate the device, and control its emission of energy within the body during tissue ablation procedures.
For example, in electrophysiological therapy, ablation is used to treat cardiac rhythm disturbances. During some of these procedures, a physician steers a catheter through a main vein or artery into the interior region of the heart that is to be treated. The physician places an ablating element carried on the catheter near the cardiac tissue that is to be ablated. The physician directs energy from the ablating element to ablate the tissue and form a lesion.
In electrophysiological therapy, there is a growing need for ablating elements capable of providing lesions in heart tissue and other tissue having different geometries.
For example, it is believed the treatment of atrial fibrillation requires the formation of long lesions of different curvilinear shapes in heart tissue. Such long lesion patterns require the deployment within the heart of flexible ablating elements having multiple ablating regions. The formation of these lesions by ablation can provide the same therapeutic benefits the complex suture patterns that the surgical maze procedure presently provides, but without invasive, open heart surgery.
As another example, it is believed that treatment of atrial flutter and ventricular tachycardia requires the formation of relatively large and deep lesion patterns in heart tissue. Merely providing "bigger" electrodes does not meet this need. Catheters carrying large electrodes are difficult to introduce into the heart and difficult to deploy in intimate contact with heart tissue. However, by distributing the larger ablating mass required for these electrodes among separate, multiple electrodes spaced apart along a flexible body, these difficulties can be overcome.
With larger and/or longer multiple electrode elements comes the demand for more precise control of the ablating process. The delivery of ablating energy must be governed to avoid incidences of unwanted tissue damage and coagulum formation. The delivery of ablating energy must also be carefully controlled to assure the formation of uniform and continuous lesions, without hot spots and/or gaps forming in the ablated tissue.